1. Technical Field
The present invention relates generally to a reflective display device and a method of manufacturing the reflective display device, and more particularly to an electrochromic photonic-crystal reflective display device and a method of manufacturing the electrochromic photonic-crystal reflective display device.
2. Description of the Related Art
Display devices may be classified into emissive display devices (e.g., an OLED display device, etc.) and reflective display devices (e.g., a photonic crystal display device, etc.). Photonic crystals have a structure in which two or more dielectric materials having different refractive indices are periodically repeated. Photonic crystals that exist in nature include opal, the wings of the Morpho menelaus butterflies, and the feathers of peacocks.
One-dimensional photonic crystals have a structure in which refractive indices are periodically repeated one-dimensionally, two-dimensional photonic crystals have a structure in which refractive indices are periodically repeated in the same plane, and three-dimensional photonic crystals have a structure in which a refractive index varies periodically in a three-dimensional space. FIG. 1 shows schematic diagrams of one-dimensional, two-dimensional, and three-dimensional photonic crystal structures.
According to the photonic crystal theory, the wavelength of reflected light is determined depending on the spacing between crystal lattices. Accordingly, when the spacing between crystal lattices is adjusted via various external stimuli, various colors of light can be obtained. Research into the application of the above phenomenon to display devices is being actively conducted. FIG. 2 is a schematic diagram showing Bragg-Snell reflection for crystal lattices.
Among photonic crystals based on organic materials, a block copolymer is a material that attracts the highest attention. A block copolymer can implement nano-structures, such as layered, cylindrical, and gyroid structures, using a phase separation phenomenon based on the interaction between polymers, can easily form a large area, and is suitable for the manufacture of a flexible device, which corresponds to the greatest advantage of a polymer material. FIG. 3 shows the states of the layered, cylindrical and gyroid nano-structures of a block copolymer (polystyrene-b-polyisoprene).
Various types of research into photonic crystals using a block copolymer have been conducted from the research mentioned in the paper published in the journal Nature in 2007. The wavelength area of reflected light is adjusted through the selective swelling of a P2VP layer via a layered structure using PS-b-P2VP (polystyrene-b-poly-2-vinylpyridine) and water. FIG. 4 is a schematic diagram of selective swelling via a PS-b-P2VP layered structure and water.
In the above-described research, a photonic crystal thin film is located in the state of being immersed in an aqueous solution. Based on the type of aqueous solution, the color of reflected light can be adjusted by selectively influencing the thickness and refractive index of one of the two different layers of photonic crystals. The changing of color using an aqueous solution has problems related to application to a display device and difficulty in manufacturing a flexible display device, which result from volatility and sealing problems.
Thereafter, first solid photonic crystals via an ionic liquid were implemented in the “macromolecules” paper. A solid photonic crystal device without a liquid was implemented by introducing an ionic liquid onto the top of a block copolymer photonic crystal via drop casting. Accordingly, problems, such as difficulty in manufacturing a flexible device, which results from volatility, inflammability, and sealing problems attributable to the use of a liquid electrolyte, could be overcome. FIG. 5 is a schematic diagram illustrating solid photonic crystals via an ionic liquid.
However, the conventional research simply implements solid block copolymer photonic crystals using an ionic liquid in the visible ray area, and is problematic in that the solid block copolymer photonic crystals do not exhibit the characteristics of an electrochromic device. Meanwhile, it is considerably difficult to implement a solid flexible block copolymer photonic crystal device that electrically reacts in response to low voltage and that is stable. The conventional research is also problematic in that it cannot implement solid flexible block copolymer photonic crystal device.